The present invention relates to a silver halide photographic light-sensitive emulsion which, for example, by being formed as an emulsion layer on a support such as film, is utilized as a photographic light-sensitive material.
In recent years, with the development of photographic technology, further increasing the sensitivity of photographic light-sensitive materials has been strongly demanded; that is, increasing the sensitivity of photographic light-sensitive materials in order to meet the respective needs of, e.g., using high shutter speeds of cameras; rapidly processing color and black-and-white photographic papers; electronically automating or simplifying the processing in the graphic arts field; lowering the medical X-ray dose; and the like.
To take the medical radiographic field as an example, those conventional regular-type X-ray films, sensitive to the wavelength region of around 450 nm, are now replaced by orthochromatic-type radiographic films, which are orthochromatically sensitized so as to be sensitive to the wavelength region of 540 to 550 nm. In those thus sensitized films, not only is the wavelength region to which they are sensitive extended but also their sensitivity to X-rays is increased, and therefore they permit reducing X-ray dose, thus enabling to minimize the influence of X-rays upon the human body.
As for the technology of increasing the sensitivity of photographic light-sensitive materials, many researches and developments have been made to date, and a number of useful means have been found. As one of them, the technique of using sensitizing dyes, i.e., the so-called "spectral sensitization" is known. The technique is very useful means for the sensitization, but has many problems yet to be solved. For example, there are cases where the spectral sensitization by use of sensitizing dyes is unable to make any adequate sensitization, depending on the type of photographic emulsion; the preservability of an emulsion after its sensitization is not enough, i.e., the sensitivity of the emulsion becomes deteriorated or color-stained with time; the sensitized emulsion tends to be sensitive to the conventional safelight thereby to be fogged; and the like,--these problems remain unsolved. Particularly, regarding the problem of the sensitized emulsion being fogged by the safelight, various measures have hitherto been taken for the applying quantity, method, etc., of sensitizing dyes to the emulsion, but such measures, on the contrary, sometimes badly impair the sensitization effect, thus making the addition of sensitizing dyes to the emulsion meaningless.
In various light-sensitive materials, even though the sensitivity thereof is raised by sensitizing means, the emulsion thereof is sometimes blackened or desensitized by various mechanical pressure applied thereto prior to being exposed (blackened trouble found after development and desensitization found during development, both being caused by mechanical pressure applied before exposure.). Particularly, medical X-ray film, because its size is large, is sometimes bent from its own weight to produce film folds such as knick marks to thereby tend to cause blackened or desensitized trouble by pressure. Lately, as the medical radiographic system, automatic exposure and developing apparatuses which use automatic transport mechanism are extensively used. In such apparatuses, mechanical force is applied to film, and the mechanical force, particularly in a dry place, tends to cause the above-mentioned blackened or desensitized trouble on the film. Such the trouble will possibly cripple the medical diagnosis.
There have until now been proposed various methods for restraining the occurrence of such blackened and desensitized troubles by pressure; for example, those methods of adding gelatin plasticizers as described in U.S. Pat. No. 3,655,390, British Pat. No. 1,307,373, U.S. Pat. No. 3,772,032, etc.; those methods of adding pressure fog-preventing agents as described in U.S. Pat. Nos. 3,655,390, 3,445,235, 2,628,167, etc,; and the like.
As the above gelatin plasticizer, the above publications describe polymer dispersoids such as latexes and hygroscopic substances, but these are considered unfavorable because they affect the sensitivity, produce fog, or adversely affect the physical property, such as the adherence of the layer to the support, of a light-sensitive material.
As the latter pressure fog-preventing agent, the above publications disclose amine-borane compounds, iridium-rhodium salts, and water-soluble bismuth salts, but these deteriorate the sensitivity.